What do you understand by the term sound energy?

In a submarine equipped with sonar,the time between the transmission of ultrasonic signals and the reception of the echo after reflection is found to be $80 \, s$. Find the distance of the obstacle from the submarine,given that the speed of sound in water is $1530 \, m s^{-1}$. (in $, m$)

$(i)$ Which property of sound wave determines:
$(a)$ loudness
$(b)$ pitch?
$(ii)$ $A$ $SONAR$ station picks up a return signal after $3 \ s$. How far away is the object? (Speed of sound in water is $1440 \ m \ s^{-1}$)
$(iii)$ How can reverberations in a big hall or auditorium be reduced?

Explain why echoes cannot be heard in a small room.

$A$ vibrating tuning fork is placed over the mouth of a burette filled with water. The tap is opened and the water level gradually falls. It is observed that the sound becomes the loudest for a particular length of air column.
$(i)$ What is the name of the phenomenon taking place when this happens?
$(ii)$ Why does the sound become the loudest?
$(iii)$ How does the frequency of the loud sound compare with that of the tuning fork?
$(iv)$ State the unit for measuring loudness.

Given that sound travels in air at $340 \, m s^{-1}$,find the wavelength of the waves in air produced by a $20 \, Hz$ sound source. If the same source is put in a water tank,what would be the wavelength of the sound waves in water? (Given,speed of the sound in water $= 1480 \, m s^{-1}$)